First we need to know what are the disks/partitions available to us in the system
List all partitions available in the system:
cat /proc/partitions
or
fdisk -l

Mount
Use command
mount <disk or partition to load> <location to load in this system>
eg:
mkdir /mnt/disk1
mount /dev/sda4 /mnt/disk1

Now one can access the sda4 partition by accessing the location /mnt/disk1
Notice that disk1 doesn't have a copy of sda4. Any changes you make here will be reflected in the data in sda4.

Unmount
To unmount use command
umount /mnt/disk1

For more information click here